1 Geographic variation and temporal trends in ice phenology in Norwegian lakes during the period 2 1890-2020 3 4 Jan Henning L’Abée-Lund1, Leif Asbjørn Vøllestad2, John Edward Brittain1,3, Ånund Sigurd Kvambekk1 5 and Tord Solvang1 6 7 1 Norwegian Water Resources and Energy Directorate, Box 5091 Majorstuen, N-0301 Oslo, Norway 8 2 Centre for Ecological and Evolutionary Synthesis, University of Oslo, Box 1066 Blindern, N-0316 9 Oslo, Norway 10 3 Natural History Museum, University of Oslo, Box 1072 Blindern, N-0316 Oslo, Norway 11 12 13 Correspondence to: Jan Henning L’Abée-Lund (
[email protected]) 14 1 15 Abstract 16 Long-term observations of ice phenology in lakes are ideal for studying climatic variation in time and 17 space. We used a large set of observations from 1890 to 2020 of the timing of freeze-up and break- 18 up, and the length of ice-free season, for 101 Norwegian lakes to elucidate variation in ice phenology 19 across time and space. The dataset of Norwegian lakes is unusual, covering considerable variation in 20 elevation (4 – 1401 m a.s.l.) and climate (from oceanic to continental) within a substantial latitudinal 21 and longitudinal gradient (58.2 – 69.9 N; 4.9 – 30.2 E). 22 The average date of ice break-up occurred later in spring with increasing elevation, latitude and 23 longitude. The average date of freeze-up and the length of the ice-free period decreased significantly 24 with elevation and longitude. No correlation with distance from the ocean was detected, although 25 the geographical gradients were related to regional climate due to adiabatic processes (elevation), 26 radiation (latitude) and the degree of continentality (longitude).